Field of the Invention
This invention relates to modified bio-derived polymers having improved process ability, and particularly improved melt strength, compared with currently available bio-derived polymers as well as methods of producing such polymers and articles produced therefrom. The polymers described herein are suitable for use in plastic processing techniques which require higher melt strength, including, but not limited to, extrusion blow molding, and blown film extrusion processing.
Description of Related Art
Bio-derived polymers are polymers that are made from renewable resources. Bio-derived polymers may be both biodegradable and biocompostable. Polylactic acid (PLA) is one such example of a bio-derived polymer that is both biodegradable and biocompostable, and it is made commercially by several companies from corn and other types of renewable resources. Because they are made from bio-renewable agricultural resources, manufacture of bio-derived polymers does not depend on depleting natural gas and oil resources for monomer feedstock. Potential market applications for these materials include biodegradable plastic bottles, packaging, disposable drink cups, plastic straws, and many other articles that are traditionally manufactured from polyethylenes, polypropylenes, polystyrenes, polyvinyl chlorides, as well as other plastics. Replacement of such traditional plastics used in these types of products with bio-derived polymers provides advantages of biodegradability, and lower carbon footprint for increased sustainability. While each of these traditional plastic materials may take tens to hundreds of years to degrade, PLA and certain other bio-derived polymers offer a much greater rate of biodegradation which generally can occur within a period of several months.
Most of the articles currently made from bio-derived polymers such as PLA are made by one or more of the major high-volume plastic processes such as fiber, film, profile or sheet extrusion, and primarily injection molding, for which the melt strength of PLA is suitable. PLA, as with many other bio-derived polymers, has not been found useful or suitable for use in plastic processes that require higher melt strength than that required for injection molding or extrusion, such as extrusion blow molding and blown film processes, both of which rely on and require the formation of a high melt strength extruded tube or parison to shape the article. Generally, the extrusion blow molding and blown film extrusion processes require use of high melt strength materials in order to maintain the parison in a highly viscous or leather-like state without undergoing too much sagging. PLA, as well as many other bio-derived polymers, are inherently low melt strength polymers, rendering them inappropriate for use in at least the extrusion blow molding and blown film processes since a parison created from these materials will usually collapse upon itself preventing formation of blown products therefrom.